February in the hills with Chris Horne and Barbara Mitcalfe

In the December article, we described the fern Asplenium bulbiferum. This month's plant choice is another common member of the asplenium genus: Asplenium polyodon. ‘Polyodon’, derived from Greek, refers to the many teeth on the margins of the frond segments.

The name ‘spleenwort’, used in part of the names for several members of the Asplenium genus, refers to a first-century AD belief that spleenworts could cure enlarged spleens.

Asplenium polyodon Photo: Jeremy Rolfe

Form, size, habitats

On your tramps in the bush you will probably have noticed sickle spleenwort’s strikingly handsome, long, arching fronds, each with many segments. Petako grows on the trunks of trees and tree ferns, or on the forest floor, or may hang down from clumps of nest-epiphytes such as species of Astelia in the crowns of large forest trees. The hanging fronds, dark green and glossy above, paler and dull below, are 150-1000 x 70-250 mm, on stalks 100-400 mm long. You may also have seen stunted petako growing on rocky surfaces.

Look closely at a segment to see the many teeth mentioned in our first paragraph. Note that each tooth may have from one to as many as sixteen serrations. A vein curves from the mid-rib to the end of each serration.

Reproduction

The segments bear the reproductive organs, sori, up to 20 mm long, which form in lines along the veins which curve away from the mid-ribs of the segments. Spores, which develop within the sori, eventually ripen, and are then carried by the wind to another location, where they may germinate.

Distribution

Petako is common in lowland to montane forests in the North Island. In the South Island, it is mainly on the western side, although it also grows in a few sites from Banks Peninsula southwards. It occurs on the Kermadecs, The Three Kings, Rakiura / Stewart, and Rekohu / Chatham islands.

It also occurs in Australia, and is widespread in the tropics from Madagascar to the Pacific islands.

Uses

We have been unable to find any references to rongoā (medicinal uses) for petako - please tell us if you read or hear about any. How about photographing the fern to show its attractive, pendulous habit, or including it in the foreground of a forest scene.